Compact process chamber for improved process uniformity

ABSTRACT

A semiconductor processing chamber, capable of withstanding low pressures while transmitting radiant energy, is provided in a lightweight, compact design. The inner surface of the window is preferably substantially flat and parallel to the wafer to be processed. The window is thin in a center portion and thicker in a surrounding peripheral portion. The thickness increases in the radially outward direction, defined between the flat inner surface and a concave outer surface. Deposition uniformity is improved by employing multiple outlet ports for distributing gas laterally in a short length, enabling a compact, symmetrical geometry. Preferably, a quadra-flow system of gas distribution is used, whereby the chamber contains one inlet port and three outlet ports distributed approximately at 90 degrees around a cylindrical side wall defining the chamber space.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/195,793, filed Nov. 19, 1998, now U.S. Pat. No. 6,143,079.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to process chambers for chemical vapor depositionand other processing of semiconductor wafers and the like. Moreparticularly, the present invention relates to cold wall processchambers capable of withstanding stresses associated with hightemperature, low pressure processes and having improved temperatureuniformity and gas flow characteristics.

2. Description of the Related Art

Process chambers for thermally processing semiconductor wafers such assilicon can desirably be made of quartz (vitreous silica) or similarmaterials which are substantially transparent to radiant energy.Reactors incorporating radiant heat lamps and reaction or processchambers with transparent walls are known in the industry as “cold wall”reactors. Thus, radiant heat lamps may be positioned adjacent theexterior of the chamber and a wafer being processed in the chamber canbe heated to elevated temperatures without having the chamber wallsheated to the same level. Quartz is also desirable because it canwithstand very high temperatures, and because it is inert, i.e., doesnot react with the various processing gases typically used insemiconductor processing.

Conventional quartz windows used in semiconductor processing chambersgenerally employ either a flat or outwardly curved configuration. Flatwindows are more commonly used when the pressure on the inside of thechamber is substantially the same as the pressure on the outside of thechamber. Flat windows have the advantage of providing a uniform heightbetween the wafer and the inside surface of the window to provide foruniform cross-sections along the flow path of process gases in chemicalvapor deposition (CVD), and hence a more laminar flow. Flatwall chambersmay also be used when the external pressure outside the chamber differssignificantly from the internal pressure within the chamber. However, insuch a chamber the windows must be very thick to resist the stresses onthe chamber. Thick flatwall chambers unfortunately require additionalmaterial and thus add weight to the reactor.

Cold wall chamber designs must also account for thermal effects. Ingeneral, the wall temperature during thermal processing should beconfined to a very small window. If the temperature gets too high,processing gases can react with one another at the wall (e.g. chemicalvapor deposition occurs on the chamber walls). Too low a temperature cancause condensation of constituent gases. In either case, clouding of thewalls can cause absorption of radiant heat, leading to cracking andcatastrophic failure.

A typical cold wall processing chamber contains a susceptor forsupporting the wafer to be processed. This susceptor is often made of aheat absorbing material, which causes the center of the chamber to runextremely hot. When the windows of the chamber are made thick to handlehigh or low pressure applications, the quartz windows absorb more heatfrom the inside of the chamber. Additionally, a greater amount ofradiant heat is absorbed when passing through thicker transparent walls.Moreover, hotter inner surfaces tend to expand more rapidly than theouter surfaces due to thermal expansion, thereby causing the window tocrack.

Forced air cooling is typically applied to the outside of the windows tokeep the chamber walls cool during processing. But thick, more massivewindows retain more heat, such that forced air cooling is less effectivefor thick windows. The high temperature at the inner surface of thewindows therefore results in chemical deposition on this surface. Inaddition, it is difficult to direct an appropriate amount of cooling airto a specific location without affecting an adjacent location. Thus, itis difficult to control wall temperature in a desired location tominimize the occurrence of localized depositions.

For applications in which the pressure within a quartz chamber is to bereduced much lower than the surrounding ambient pressure, the strengthof the chamber walls becomes important. Dome-shaped chambers have beendisclosed, for example, in U.S. Pat. Nos. 5,085,887 and 5,108,792. U.S.Pat. No. 5,085,887 discloses a chamber which includes an upper wallhaving a convex outer surface and a concave inner surface. A greatlythickened peripheral flange is provided to radially confine the upperwall, causing the wall to bow outward due to thermal expansion, helpingto resist the exterior ambient pressure in vacuum applications. Thechamber requires a complex mechanism for clamping the thickened exteriorflanges of the upper and lower chamber walls.

A lenticular chamber has been described in a pending applicationentitled PROCESS CHAMBER WITH INNER SUPPORT, Ser. No. 08/637,616, filedApr. 25, 1996, now U.S. Pat. No. 6,093,292, the disclosure of which isincorporated by reference. This chamber has thin upper and lower curvedwalls having a convex exterior surface and a concave interior surface inthe lateral dimension, with constant longitudinal cross-sections(longitude being defined by the axis internal of gas flow). These wallsare joined at their side edges by side rails, thus giving the chamber agenerally flattened or ellipsoidal cross-section. The chamber upper andlower walls are generally rectangular in shape, such that a waferdisposed within the chamber is located farther from the upstream anddownstream ends than from the lateral side rails.

The rectangular shape of the lenticular chambers is advantageous inkeeping elastomeric O-rings located at the longitudinal ends of thechamber farther away from the center of the chamber where the wafer islocated. These O-rings have a tendency to heat up, and therefore, iflocated too close to the susceptor/wafer combination at the center ofthe chamber, they will become difficult to cool and may burn more easilydue to exposure to high temperatures. Moreover, a rectangular shapeevenly distributes gas flow through the chamber. By providing a longerlongitudinal distance for gas to flow over the wafer to be processed,the gas can spread out in the chamber before reaching the wafer, therebyallowing a more uniform deposition.

While these lenticular chambers present a good design for low pressureapplications, scaling this design to larger sizes presents difficulties.A lenticular chamber designed to accommodate a 200 mm wafer has a lengthof about 600 mm, a width of about 325 mm, and a chamber height of about115 mm. To increase the chamber size for a 300 mm wafer, whilemaintaining relatively the same rectangular proportions, the chamberwould have to have a length of about 900 mm and a width of about 488 mm.Such a chamber is big and heavy, and more difficult to fabricate,requiring special cranes and lifting devices. The increased footprintalso decreases the amount of clean room space available. Furthermore,the larger size makes the chamber more difficult to clean.

Lenticularly-shaped chambers could also be improved to favor a moreuniform deposition of material. In such chambers, the quartz walldisposed over the wafer to be processed is curved, creating a greaterchamber volume above the center of the wafer than over the lateraledges, such that uniform deposition is difficult to achieve.

Deposition. uniformity is affected by the gas flow profile produced overthe wafer, both in lenticular and other types of chambers. There havebeen attempts to control the gas flow profile in parallel across thewafer to be processed, to create a more uniform deposition. For exampleU.S. Pat. No. 5,221,556 discloses a system in which the apertures of thegas inlet manifold are varied in size to allow relatively more gasthrough a particular section, typically the center section. U.S. Pat.No. 5,269,847 includes valves for adjustment of pairs of gas flowsmerging into a number of independent streams distributed laterallyupstream of the wafer to be processed. This system emphasizes theimportance of channeling the various gas flows separately until justbefore the wafer leading edge in order to prevent premature mixing andenable greater control over the flow and concentration profiles ofreactant and carrier gases across the wafer.

Despite recent advancements, a need still exists for a processingchamber with an improved design. Preferably, such a chamber shouldexhibit uniform deposition. At the same time, the chamber should belightweight and compact, but still able to withstand pressuredifferentials and high temperatures, particularly for wafers 300 mm andlarger. Furthermore, this chamber should be made lightweight and strongwithout subjecting the chamber to depositions or cracking due to thermaleffects.

SUMMARY OF THE INVENTION

A semiconductor processing chamber is provided for use at either low orambient pressures with a compact size which runs cleaner and produces amore uniform deposition profile than the chambers of the prior art. Theinner surface of the window is preferably substantially flat andparallel to the wafer to be processed, creating a uniform space abovethe wafer to lead to a more even deposition of material. The window isthin in a center portion and increases in thickness as determined by anouter surface having a substantially concave shape. Depositionuniformity is improved by employing multiple outlet ports fordistributing gas throughout the chamber. Preferably, the reactor employsa multiple-port system of gas distribution. In the disclosed embodiment,the chamber contains one inlet port and three outlet ports distributedapproximately at 90 degrees around a cylindrical side wall defining thechamber space.

In accordance with one aspect of the present invention, a singlesubstrate thermal processing chamber is provided with a first wall and asecond wall. The first wall is substantially transparent to radiantheat, having a center portion which is thinner than a peripheral portionsurrounding the center portion. The second wall similarly includes athin center portion. A side wall connects the first and second walls todefine a chamber space surrounded by the walls. A substrate supportstructure is positioned within the chamber space.

In accordance with another aspect of the present invention, a chamber isprovided with a window which allows transmission of radiant heat to asubstrate supported within the chamber. The window has a center portionand a thicker surrounding peripheral portion.

In accordance with another aspect of the present invention, a reducedpressure chamber for processing a semiconductor wafer is disclosed. Thischamber includes a window allowing transmission of radiant heattherethrough to a wafer to be processed. The window has inner and outersurfaces for facing the wafer and a radiant heat source, respectively,during processing. The outer surface includes a concavely shapedsection.

In accordance with another aspect of the present invention, a cold wallthermal processing reactor is provided. The reactor includes at leastone radiant heat lamp, a substrate support structure, and a windowdisposed between the radiant heat lamp and the substrate supportstructure. The window has a center portion and a peripheral portion,both of which allow transmission of radiant heat from the lamp to thesubstrate support structure. The center portion is thinner than theperipheral portion.

In accordance with another aspect of the present invention, asemiconductor processing chamber is provided. The chamber walls define adeposition chamber, and a substrate support is positioned within thechamber for horizontally supporting a single semiconductor substrate. Agas inlet is disposed in the walls of the chamber for producing gas flowinto the chamber. At least two gas outlets are disposed in the walls ofthe chamber for exhausting gas flow from the chamber.

In accordance with another aspect of the present invention, a gas systemfor processing semiconductor wafers is provided. The system includes achamber having an upstream end and a downstream end, with an inlet portlocated at the upstream end of the chamber for releasing processinggases into the chamber. A primary outlet port is located at thedownstream end of the chamber for removing processing gases from thechamber to produce gas flow in a longitudinal direction across thewafer. A pair of secondary outlet ports is located in a sidewallconnecting the upstream and downstream ends for removing processinggases from the chamber.

In the preferred embodiment, the secondary outlet ports are positionedand configured to minimize gas recirculation within the chamber. Suchrecirculation can cause process non-uniformity and chamber coatingswhich affect the overall cleanliness of current state-of-the-artsystems.

In accordance with another aspect of the present invention, a cold wallprocessing reactor is provided with a window between a plurality ofradiant heat lamps and a susceptor designed to hold a semiconductorwafer. The window has an inner surface facing the susceptor and an outersurface facing the heat lamps. The window includes a first portion,which is relatively close to a center axis of the susceptor, and secondportion, which is farther from a center axis of the susceptor. Theminimum thickness of the first portion is smaller than the minimumthickness in the second portion.

In accordance with another aspect of the present invention, a method isprovided for producing a uniform gas flow across a semiconductor waferbeing processed in a reaction chamber. This method includes tuning thegas flow out of the chamber through a plurality of outlet ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front, top and side perspective view of a processing chamberconstructed in accordance with a preferred embodiment of the presentinvention.

FIG. 2 is a side sectional view along lines 2—2 of FIG. 1.

FIG. 3 is a top-down sectional view along lines 3—3 of the processingchamber shown in FIG. 1, illustrating possible gas flow paths throughthe chamber.

FIG. 4 is an exploded perspective view showing assembly of theprocessing chamber of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the chamber described herein is applicable to batch processingsystems, it is of particular utility in single wafer processing systems.In particular, the chamber 10 described herein is applicable toprocessing of a single 300 mm silicon wafer at a reduced pressure ofabout 20 to 60 Torr. It should be recognized, however, that theprinciples of the present invention are applicable to other size wafersprocessed at different pressures and temperatures. The skilled artisanmay also find application for the principles disclosed herein to bothcold wall and hot wall reactors. Furthermore, advantages of the chamberdescribed herein are applicable to several types of processing,including thermal annealing, deposition, etching, lithography,diffusion, and implantation.

Preferred Chamber

FIGS. 1 and 2 show a semiconductor processing reactor 8, which includesa reaction or process chamber 10, constructed in accordance with apreferred embodiment. The chamber 10 has an upper wall 12 and a lowerwall 14 defining a chamber space 16 between the two. The upper and lowerwalls 12, 14 are connected by a side wall 18 surrounding the chamberspace 16. A flange 20 further surrounds the side wall 18.

As described in further detail below, a system of multiple gas ports isprovided in the chamber. The illustrated embodiment shows an inlet port22, a primary or main outlet port 24, a first side outlet port 26, and asecond side outlet port 28 (shown in FIG. 3), provided through theflange 20 and side wall 18 to allow entry and exhaust of processinggases to and from chamber space 16. The inlet 22 is also sized to allowentry and removal of a semiconductor wafer 56. The primary direction ofgas flow defines a longitudinal direction, extending from an upstream toa downstream end, where the upstream end corresponds to the location ofthe gas inlet port 22, and the downstream end corresponds to thelocation of the main gas outlet port 24, positioned opposite the inletport 22. A lateral direction is oriented perpendicular to thelongitudinal direction. The illustrated side ports 26 and 28 are locatedin the side wall 18, opposite each other and approximately 90 degreesfrom the inlet and outlet ports 22 and 24, respectively. Thus, in theillustrated embodiment, the lateral direction extends from the firstside outlet port 26 to the second side outlet port 28.

Preferably, at least portions of the upper wall 12 and the lower wall 14are transparent to radiant heat energy, and preferably comprise quartz.The transparent portions of the walls 12, 14 through which radiantenergy actually passes during processing can be referred to as“windows.” Although quartz is the preferred material for the upper andlower windows, other materials having similar desirable characteristicsmay be substituted. Some of these desirable characteristics include ahigh melting point, the ability to withstand large and rapid temperaturechanges, chemical inertness and high transparency to radiant heat.

As shown in FIG. 2, the chamber forms part of a reactor 8. A pluralityof radiant heat sources are supported outside the chamber 10, to provideheat energy to the chamber 10 without appreciable absorption by thequartz chamber walls. While the preferred embodiments are described inthe context of a “cold wall” CVD reactor for processing semiconductorwafers, it will be understood that the processing methods describedherein will have utility in conjunction with other heating/coolingsystems, such as those employing inductive or resistive heating.

The illustrated radiant heat sources comprise an upper heating assemblyof elongated tube-type radiant elements 89. The upper heating elements89 are preferably disposed in spaced-apart parallel relationship andalso substantially parallel with the process gas flow path through theunderlying reaction chamber 10 as described below. A lower heatingassembly comprises similar elongated tube-type radiant heating elements90 below the reaction chamber 10, preferably oriented transverse to theupper heating elements 89.

Desirably, a portion of the radiant heat is diffusely reflected into thechamber 10 by rough specular plates (not shown) above and below theupper and lower lamps 89, 90, respectively, while some of lamps 89, 90are backed by curved reflectors (not shown) to direct concentrated heat.Additionally, a plurality of spot lamps 91 supply concentrated heat tothe underside of the wafer support structure (described below), tocounteract a heat sink effect created by support structures extendingthrough the bottom of the reaction chamber 10 to the relatively colderenvirons.

Each of the elongated tube type heating elements 89, 90 is preferably ahigh intensity tungsten filament lamp having a transparent quartzenvelope containing a halogen gas, such as iodine. Such lamps producefull-spectrum radiant heat energy transmitted through the walls of thereaction chamber 10 without appreciable absorption. As is known in theart of semiconductor processing equipment, the power of the variouslamps 89, 90, 91 can be controlled independently or in grouped zones inresponse to temperature sensors.

As shown in FIG. 3, the flange 20 defining the horizontal perimeter ofthe chamber 10 has a generally rectangular shape with chamfered corners.The flange 20 may also be square, circular, or any other shape that willaccommodate a compact design for processing a wafer in a small space.The flange 20 is preferably made of 316L stainless steel, and is watercooled during processing in any suitable manner, as will be readilyappreciated by one of skill in the art. As shown in FIG. 2, O-rings 126are provided between the side wall 18 and flange 20. The side wall 18 ispreferably made of opaque quartz. Opaque quartz is preferred for theside wall to reflect radiant energy away from the metal flange 20 andback to the chamber, to protect the flange 20 and the O-rings 126 fromextreme temperatures.

For a wafer 56 having a diameter of about 300 mm processed at a pressureof about 20 torr, the chamber 10 has a length in the longitudinaldirection, as measured from the ends of flange 20, preferably of about15 to 30 inches, and more preferably about 23 inches. The width offlange 20 in the lateral direction is preferably about 15 to 30 inches,and more preferably about 22 inches. The height of flange 20 ispreferably between about 3 to 6 inches, and more preferably, about 4inches. The inner diameter of the flange 20, corresponding to the outerdiameter of side wall 18, is preferably about 14 to 22 inches, and morepreferably, about 18 inches. The side wall 18 has an inner diameterpreferably of about 12 to 21 inches, and more preferably, about 16.75inches. The height of side wall 18 is preferably about 2 to 5 inches,and more preferably, about 3.25 inches.

The preferred embodiment thus enables processing a single 300 mm waferwith a small reactor 8 footprint. In the illustrated embodiment, theouter dimensions of the flange 20 define a footprint of less than about3,300 cm², whereas the process chamber area, defined by the innerboundaries of the side wall 18, is less than about 1,500 cm². Despitethe compact size and design which avoids recirculation, the novelchamber design enables reduced or low pressure processing, preferably atless than about 100 Torr, and more preferably less than about 60 Torr.

Wafer Support Structure

As shown in FIG. 2, the chamber 10 is divided into an upper section 30and a lower section 32 by a wafer support structure which comprises agenerally flat circular susceptor or wafer holder 36, which supports thewafer 56. The susceptor 36 is located approximately in the center of thechamber 10, and is surrounded by a ring 38, sometimes referred to as atemperature compensation ring or a slip ring. The slip ring 38 can beused to house thermocouples 39, as illustrated, and also to absorbradiant heat during high temperature processing. This compensates for atendency toward greater heat loss at the edges of wafer 56, a phenomenonwhich is known to occur due to a greater concentration of surface areafor a given volume near such edges. By minimizing edge losses and theattending radial temperature non-uniformities across the wafer 56, theslip ring 38 reduces the risk of wafer crystallographic slip or otherconsequences of non-uniform temperatures during processing.

As shown in FIG. 2, the susceptor 36 and slip ring 38 are positioned ona plane just below the inlet and outlet ports 22, 24, 26 and 28. Asacrificial or divider plate 34 is provided surrounding the ring 38,preferably comprising quartz. This plate 34 serves to confine gas flowto the upper section 30, thereby producing better laminar flow. Thesacrificial plate 34 has an inner diameter which closely conforms withthe outer diameter of the ring 38, and an outer shape which conformswith and desirably abuts against the side wall 18. In this manner, theside wall 18 is protected from devitrification from repeated heating ofthe reaction chamber 10. This enables the sacrificial plate 34 to bereplaced when it devitrifies from repeated heat cycles, while preservingthe more expensive side wall 18. The plate 34 is preferably supported byledges formed in the side wall 18, and is preferably located in the sameplane as the susceptor 36. The ring 38, in turn, is supported bybrackets 84 extending from the plate 34. Alternatively, the slip ringcould be supported by a stand resting on the lower chamber wall, or byledges extending inwardly from the chamber side walls.

The susceptor 36 is supported by a spider 40 having three arms extendingradially outward from a central hub and having upwardly extendingprojections on the ends of the arms engaging the susceptor. Thesusceptor 36 may also be provided with one or more recesses (not shown)on its lower surface for receiving the ends of the projections tofacilitate centrally positioning the susceptor and forming a couplingwith the spider 40 for rotating the susceptor. The spider 40 is mountedon a shaft 42 which extends through the chamber lower wall 14 and alsoextends through a tube 44 integrally attached to and depending from thelower chamber wall 14. The shaft 42 is connected to a drive motor (notshown) for rotating the shaft 42, the spider 40, and the susceptor 36.Details of a similar arrangement together with a drive mechanism may beseen in U.S. Pat. No. 4,821,674, the disclosure of which is incorporatedherein by reference.

The susceptor 36 and preferably the slip ring 38 are made from amaterial which can withstand high temperature processing. Desirably,this material is one that does not devitrify, is a good absorber ofradiant energy, is a reasonably good thermal conductor, has goodresistance to thermal shock, and is durable and compatible with thevarious materials and chemicals used in processing. The illustratedsusceptor 36 and slip ring 38 comprise silicon carbide. Other potentialmaterials include boron nitride, silicon nitride, silicon dioxide,aluminum nitride, aluminum oxide, combinations or compounds of thesematerials, pyrolytic graphite and other similar high temperature ceramiccompounds.

Design of the Upper and Lower Chamber Walls

As shown in FIG. 4, the upper and lower walls 12 and 14 are preferablysubstantially circular in shape. While in other arrangements, walls ofother shapes may also be used, such as rectangles and squares, the roundshape advantageously reduces the material costs, weight, and footprintof the reactor 8. Preferably, the wafer 56, as shown in FIG. 3, issubstantially circular in shape and is disposed directly below upperwall 12 and above lower wall 14, such that the wafer 56, the upper wall12, and the lower wall 14 all share a central axis 92, as shown in FIGS.2 and 4.

Referring to FIG. 2, in the preferred embodiment, the upper wall 12 ofchamber 10 has an inner surface 46 which is substantially planar orflat. The planar inner surface 46 of upper wall 12 is substantiallyparallel to the wafer 56, producing a substantially uniform distancefrom the upper wall 12 to the wafer 56 and to the divider plate 34. In acenter portion 48 of the upper wall 12, an outer surface 50 of chamber10 is also planar to produce a planar center portion 48 of substantiallyuniform thickness.

The center portion 48 preferably is circular in shape, but other shapesmay be used as well. The center portion 48 is preferably centered alongthe same central axis 92 as the wafer 56 and the upper and lower walls12 and 14. Extending outward from the flat center portion 48, the upperwall has a varying thickness. Preferably, the thickness increasesoutwardly in a peripheral portion or outer ring 52 surrounding thecenter portion 48 until it reaches the edge 54 of the upper wall 12. Atthe edge 54 the upper wall 12 has a constant thickness. The centerportion 48 is preferably smaller in diameter than the largest wafer forwhich the chamber 10 is designed (300 mm in the illustrated embodiment),such that the peripheral portion 52 having a greater thickness than thecenter portion is disposed at least partly above the wafer 56 to beprocessed. This arrangement enables thermal advantages for the windowwhile allowing structural support for high or low pressure applications.It will be understood, of course, that the same chamber 10 can beutilized to process smaller wafers.

The thickness of the upper wall 12 increases from the perimeter of thethin center portion 48 to the outer edge 54 in thicker peripheralportion 52, as shown in FIG. 2. This increasing thickness preferablygives the upper wall 12 a concave-outward curvature on the outer surface50 in peripheral portion 52. Unwanted stresses are introduced in curvedwalls with varying radii and thus, a circular wall with a regular orconstant curvature is desirable. In the illustrated embodiment, thethickness of the upper wall 12 in the peripheral portion 52 is definedbetween the planar inner surface 46 and the outer surface 50 whichconforms to a toroidal shape. In other arrangements, however, thethickness may increase in the peripheral portion in accordance withdifferent configurations. For instance, the thickness of the upper wall12 may gradually increase linearly or by steps, Other configurationsinclude inner or outer surfaces conforming to spherical, toroidal,elliptical, parabolic, and hyperbolic shapes.

Preferably, for a 300 mm (about 11.8 inch) processing chamber, the upperquartz wall 12 has a diameter of about 14 to 22 inches, and morepreferably about 18 inches. At the flat center portion 48, the wall 12preferably has a thickness of about 0.12 inch to 0.35 inch, morepreferably about 0.2 inch to 0.3 inches, and is about 0.25 inch in theillustrated embodiment. The diameter of flat center portion 48 ispreferably about 6 to 12 inches, and more preferably about 9 inches. Theedge 54 has a constant thickness of about 1 to 2 inches, and morepreferably, about 1.4 inches, extending over a radial length of about0.5 to 1.5 inches, more preferably about 0.87 inches. The inner surface46 of upper wall 12 is preferably about 0.5 to 2 inches above the wafer56 to be processed, more preferably about 1 inch. The increase inthickness of the upper wall 12 in peripheral portion 52 is determined bythe outer surface 50 having a radius of curvature in the verticaldimension of about 5 to 40 inches, more preferably about 8 inches.

As shown in FIG. 2, the lower wall 14 also has a substantially flat orplanar inner surface 58 but, unlike the upper wall 12, has acontinuously curved concave outer surface 60. This gives the lower walla center portion 62 which is thinner than a peripheral portion 64. Thelower wall 14 has a varying thickness which gradually increases towardsan outer edge 66, as preferably determined by the outer surface 60 whichhas a concave shape with a substantially constant radius of curvature.For the chamber 10 shown in FIG. 2, designed for processing a 300 mmwafer, this radius of curvature is preferably about 20 to 60 inches,more preferably about 40 inches. At the edge 66 the lower wall 14 has aconstant thickness. The lower quartz wall 14 preferably has a diameterof about 14 to 22 inches, and more preferably about 18 inches. At thecenter portion 62 of the wall 14, the minimum thickness can be asdescribed above for the upper wall 12. At the edge 66, the lower wallpreferably has a constant thickness of about 0.5 to 1.5 inches, morepreferably about 0.88 inches.

The shape of the upper and lower walls 12 and 14, each with an innersurface which is substantially planar and an outer surface with at leasta section which is concavely curved, is preferably manufactured bygrinding away a center portion of a thick, flat quartz plate. The quartzside wall 18 has a generally cylindrical shape and can be made bycutting a cylindrical tube made of quartz or similar material. Othermethods for manufacturing the quartz parts (or other suitable materials)will be readily apparent to those skilled in the art.

Although the chamber 10 shown in FIGS. 1-4 has been described withrespect to a certain preferred configuration and certain dimensions, theinvention is not intended to be limited to this embodiment. In otherarrangements, the upper wall may be shaped as described for theillustrated lower wall 14, and similarly, the lower wall may be shapedas described for the illustrated upper wall 12. Thus, the outer surfacesof either or both the upper and lower walls can be continuously concavein shape, and either or both can have a flattened or planar centerportion. Furthermore, the upper and lower walls may simply comprise acenter portion which is thinner than a surrounding peripheral portion.Moreover, the lower wall may simply be substantially flat and uniformlythick throughout, while the upper wall has varying thickness. Varyingthickness in the upper or lower walls can be determined by a variety ofshapes and curvatures, including, but not limited to, spherical,toroidal, elliptical, parabolic, and hyperbolic configurations. Variousother combinations of upper wall and lower wall configurations will bereadily apparent to the skilled artisan, in light of the presentdisclosure.

Process Chamber Assembly

Assembly of the process chamber is shown in an exploded perspective viewin FIG. 4. More particularly, FIG. 4 shows assembly of the upper wall12, sacrificial plate 34, side wall 18, flange 20, susceptor 36, slipring 38, lower wall 14, and tube 44. The flange 20 is comprised of aninlet flange 108 and an outlet flange 110, which are joined around theside wall 18.

In practice, the chamber 10 can be easily assembled and disassembled onsite. For example, the inlet flange 108 can be first mounted to theframe of a reactor cabinet. The quartz side wall 18 is then slid intothe inlet flange 108 with the elongated slot 68 aligned with theaperture 70 within the flange 18, thus defining the inlet port 22 (seeFIGS. 2 and 3). As shown, the side wall 18 includes an annular recess toreceive an annular ring extending inwardly from the inlet flange 108.

The outlet flange 110 can then be fitted onto the side wall 18 in asimilar fashion, until the outlet flange 110 contacts the inlet flange108 and can be bolted or otherwise fastened together. The lower wall 14,susceptor support (not shown) and susceptor 36 can then be installed insequence, and the appropriate joints sealed against process gas leakage.The quartz ring 34 sits on an annular ledge provide on the inner surfaceof the side wall 18, just below the slots 68, 72, 76, 80. The ring 34,which includes brackets 84 best seen in FIG. 2, supports the slip ring38 surrounding the susceptor 36. The upper wall 12 is then fitted ontothe side wall 18, supported by the outer edge 54 of the wall 12. Exhaustmanifolds (not shown) and valves can then be installed to receiveeffluent gases through the ports 24, 26, 28.

The chamber 10 is thus field assembleable, thereby eliminating the needfor expensive welded chambers. Due to the field assembleable feature,the chamber geometry can be changed easily. Thus, different upper andlower walls 12 and 14 may be provided to the chamber to producedifferent thermal effects and other desired characteristics for thechamber 10. Moreover, the susceptor 36 and sacrificial plate 34 can bequickly and easily replaced by removal of the upper wall 12.

Inlets and Outlets for Improved Gas Flow

The preferred chamber 10 also provides improved gas flow distribution byemploying multiple outlet ports. These ports are distributed around thechamber 10 to spread out the flow of processing gases. Preferably, atleast some of these outlet ports include variably openable valves totune the flow out of the chamber 10. Moreover, the outlet ports arepreferably symmetrically distributed in the chamber to facilitateuniform, laminar flow and reduce recirculations.

The illustrated chamber 1Q of the preferred embodiment includes four gasports (one inlet 22 and three outlets 24, 26, 28). As shown in FIG. 3, awafer 56 (shown in phantom) is disposed horizontally in the center ofchamber 10. The gas inlet port 22 is provided at the upstream end of thechamber 10. This port 22 allows entry into the chamber 10 of reactiongases as well as the wafer 56. At the downstream end, opposite the inletport 22, the primary or main outlet port 24 is provided for exhaust ofthe processing gases. The side ports 26 and 28 are located at the samevertical level as the inlet port 22 and the main outlet port 24. Thus,all four gas ports are positioned at or about a common horizontal plane.Preferably, the side outlet ports 26 and 28 are located approximately 90degrees from the ports 22 and 24 along the substantially cylindricalside wall 18 of chamber 10, and approximately 180 degrees apart fromeach other. Accordingly, a line joining the side ports 26 and 28 isapproximately transverse to the longitudinal primary flow of processinggases.

Apertures for the inlet and outlet ports are machined into the side wall18 of the preferred quartz materials. Inlet port 22 is defined by ahorizontal elongated slot 68 machined into the side wall 18, which mateswith an aperture 70 in flange 20. The slot 68 allows wafer insertion.The slot also permits the introduction of processing gases after anisolation valve (not shown) between the slot 68 and a wafer handlingchamber (not shown) has been closed. Similarly, at the three outletports 24, 26 and 28, corresponding horizontal slots 72, 76 and 80 aremachined into the side wall 18, mating with apertures 74, 78 and 82,respectively, in the flange 20 when the chamber 10 is assembled.Alternatively, the quartz side wall can be molded with apertures. Theoutlet ports allow exhaust of process gas from the chamber 10, as wellas the application of a vacuum to the chamber.

Referring now to FIG. 2, a gas injector 112 is positioned upstream ofthe process chamber 10 and includes a plurality of reactant gas flowneedle valves 114 for controlling the flow of process gases into thechamber through multiple ports. The gas injector may be of a typedescribed in a pending application entitled PROCESS CHAMBER WITH INNERSUPPORT, Ser. No. 08/637,616, filed Apr. 25, 1996, the disclosure ofwhich is incorporated by reference. Gases are metered through theinjector 112 in a downward direction indicated by arrow 116, andthereafter passes through the inlet port 22 leading into the uppersection 30 of the process chamber 10. Gas flow outside the chamberthrough the port 22 is prevented by a gate valve or door (not shown).The gate valve is open only during wafer transfer, during which processgases are not flowing. While the illustrated embodiment of FIG. 2 showsthe injector 112 extending through the flange 20, it will be understoodthat, in other arrangements, injectors can be arranged in a separateoutside flange which interfaces with the gate valve.

The gas flow into the chamber is indicated by the arrow 94. The gas flowmoves generally longitudinally across the wafer 56, primarily due to adecreasing pressure gradient along the chamber in the direction of avacuum source (not shown) downstream at the outlet port 24 for lowpressure applications. It will be understood by one of skill in the art,however, that gas flow can also be maintained in the absence of vacuumpump. At the outlet port 24, an exhaust apparatus 120 is provided forreceiving the exhaust gases.

As shown in FIG. 2, at the main outlet port 24, the gas flowcommunicates with an exhaust conduit 122 according to arrow 106, leadingto an exhaust manifold 124 which is attached to a suitable source ofvacuum. Alternatively, condensation at a downstream scrubber can assistflow-through of the exhausted gases.

Referring to FIG. 3, gas flow through the outlet ports can be adjustedor tuned through the use of valves (not shown). Preferably, the valvesare of a type which can be selectively opened and closed to produce apressure gradient from the inlet port 22 to these outlet ports, andthereby regulate gas flow. Any suitable adjustable valve means, such asbellows-type, ball valves, butterfly valves, etc., can be employed forthis purpose, as will be understood by the skilled artisan. All threeexhaust ports 24, 26, 28 are plumbed to a common port from the valves.

In the preferred embodiment, variably adjustable bellows-type valves aredisposed at the side outlet ports 26 and 28, but not at the main outletport 24. Thus, gas flows primarily longitudinally through the chamber,as indicated in FIG. 2 by a gas inlet flow arrow 94 and a gas outletflow arrow 106. In addition, secondary gas flow branches laterally offthe primary gas flow path, as shown by arrows 96 and 98. By tuningvalves at these side outlet ports 26, 28, the gas flow can be spread ornarrowed within the chamber 10 to provide a better distribution of gasesand a more even process treatment. In another embodiment, plates withfixed orifices, optimaly sized for a desired gas flow pattern, are usein place of adjustable valves at the secondary exhaust ports 26, 28.

Processing with this chamber 10 is now described in the context of anexemplary chemical vapor deposition (CVD) process. It will beunderstood, however, that the preferred chamber will also beadvantageous for other non-CVD processing. Initially, process gasesenter the chamber 10 at an ambient, non-reacting temperature and areheated to a temperature suitable for deposition as they pass over thesusceptor and wafer. The radiant heat lamps 89, 90, 91 heat the wafer56, either directly or by way of the susceptor and the slip ring. Thesurrounding slip ring 38 is a high heat absorbency material, allowingthe ring to preheat the reactant gas stream before it reaches theleading edge of the susceptor, and subsequently, the leading edge of thewafer. The preheated process gases thus readily react at the wafersurface, which is at the desired reaction temperature.

As shown in FIG. 2, purge gas is supplied upward through the hollow tube44 surrounding the shaft 42. The purge gas enters the lower portion 32as indicated by arrows 100. The purge gas inhibits process gases fromflowing around the edges of the susceptor 36 into the lower section 32,thus inhibiting unwanted deposition of particulates underneath thesusceptor 36. The bulk of this purge gas exits through the lowerlongitudinal aperture 102 near the outlet port 24 (beneath the plate34), as indicated by arrow 104. The purge gas then mixes with the spentreaction gas and continues downward through the exhaust conduit 122.Purge gas ports may also be provided below the inlet or other outletports provided in the side wall 18.

In the illustrated embodiment, for processing a 300 mm wafer, the inletport 22 preferably has a length of about 12 to 15 inches, and morepreferably about 13.25 inches, and a height preferably of about 0.5 to1.5 inches, and more preferably, about 1 inch. The main outlet port 24preferably has a length of about 12 to 15 inches, and more preferably,about 13 inches, and a height preferably of about 0.2 to 1 inch, andmore preferably, 1.5 inch. The side outlet ports 26 and 28 eachpreferably have a length of about 2 to 10 inches, and more preferably,about 5.5 inches, and a height preferably of about 0.2 to 1 inch, andmore preferably, about 0.5 inch.

While the invention discussed herein describes a preferred embodimentwith one inlet port and three outlet ports located approximately 90degrees apart, it should be recognized that a gas flow system utilizingfewer or additional ports may be employed without deviating from theessential design of the invention. For example, a “main” gas outlet neednot be provided at the downstream end of the chamber. Even for reactorswith the disclosed quadra flow structure, the main gas outlet need nothandle the majority of the exhaust flow. Chambers with two, four or moreoutlet ports can be utilized, these ports located at various locationswithin the chamber to control gas flow. Furthermore, any or all of theoutlet ports can be provided with valves or plates with orifices of afixed size for tuning the distribution of gas flow within the chamber10.

Reduced Pressure Applications

The chamber 10 designed as described above offers several advantagesover previously known processing chambers. First, the chamber utilizes asubstantially thin wall configuration while still being able towithstand compressive stresses due to low pressure processing. Finiteelement analysis shows that a chamber having a thin wall disposed over awafer to be processed, with an increasing thickness towards an outeredge, will have sufficient strength for reduced pressure processing. Aquartz window having a substantially planar inner surface and asubstantially concave outer surface has been found to be a particularlystrong design. Preferably, the chamber can withstand pressuredifferentials of greater than 0.5 atm., and more preferably about 1 atm.

In the illustrated preferred embodiment, the upper chamber wall 12 has auniformly thick center portion 48, and a peripheral portion 52 withgreater thickness than in the center portion. This peripheral portion 52preferably is disposed at least partly above the wafer 56 in order toprovide strength to chamber 10 near the center of the chamber. Forexample, the ratio of the center portion 48 to the diameter of the wafer56 can be about 0.75. Similarly, the lower wall 14 has a planar innersurface 58 and a concave outer surface 60 to give the wall 14 anincreasing thickness from a center portion 62 to an outer edge 66,thereby giving the chamber 10 sufficient strength in the lower wall towithstand compressive stresses due to low pressure processing.

Thermal Effects

During conventional processing of a semiconductor wafer in a cold wallreactor, the walls of a chamber are substantially transparent to radiantheat emitted from the lamps 89, 90, 91, such that radiation will passthrough the walls without significant absorption. This radiation thenheats the wafer and susceptor disposed inside the chamber. Once heated,the wafer and susceptor will re-radiate energy toward the walls. Becausethis re-radiated energy is of lower frequency than the IR energy comingdirectly from the lamps, the quartz windows tend to absorb thisre-radiated energy. The thicker the quartz material, the more heat thatis retained in the walls. Heating of the walls causes thermal expansionforces which can cause cracking or failure of the walls, particularlywhere different sections of a wall are heated to different degrees.Furthermore, inadequate control over the temperature of the walls canlead to deposition of reactant gases on the inner surfaces of the walls.

When processing a semiconductor wafer in a chamber with upper and lowerwalls at high temperatures, the most intense heat is re-radiated fromthe susceptor and wafer toward the center portions of the upper andlower walls closest to the wafer, while less intense heat is directedtoward the peripheral portions of the upper and lower walls. The designof chamber 10 of the present invention accounts for this heatdistribution in order to control the temperature of the walls byproviding the upper and lower walls 12 and 14 with a thinner centerportion and a thicker peripheral portion. Because thinner walls do notretain heat as much as thicker walls, varying the thickness of the wallsaccording to the intensity of heat emitted from the susceptor and wafercan help to control the temperature of the upper and lower walls.Therefore, the upper and lower walls are made thinner in their centerwhere greater heat is directed, and thicker in their periphery whereless heat is directed.

The varying thickness of the upper and lower walls enables effectivecooling by forced air or liquid cooling. During high temperatureprocessing of a wafer 56, the chamber 10 is provided with cooling airacross the outer surfaces 50 and 60 of upper and lower walls 12 and 14,respectively, to cool the inner surfaces 48 and 58. Because heatre-radiated from the wafer and susceptor is more intense at the centerportions of the upper and lower walls, these center portions areadvantageously made thinner so that the air has a larger effect oncooling the walls. Toward the peripheral portions of the upper and lowerwalls, by contrast, less heat is re-radiated from the wafer andsusceptor, and the walls require less cooling from the air and thereforecan be made thicker. It will be understood that quartz walls can also beprovided with throughbores running parallel to the wall surfaces,through which cooling liquid can be circulated.

Thus, the chamber 10 of the present invention is preferably designed tohave upper and lower walls of varying thickness, where the thicknessesof the walls. is determined to provide control over the temperature ofthe inner surfaces of the walls. This temperature control is ofparticular utility in reducing chamber wall deposits during chemicalvapor deposition (CVD). The walls of chamber 10 would be kept in thecorrect temperature range to prevent coatings deposited on the innerwalls. If the inner surface of the chamber walls gets too hot,deposition can occur by decomposition of reactant gases. For example,silane can decompose and deposit silicon on hot chamber surfaces. Ifcooled too much, process gas condensation can contaminate the innerwall. For example, silane, trichlorosilane or other silicon source gasescan condense upon overly cooled chamber surfaces. Controlling the walltemperature by varying the wall thickness thereby reduces deposition ofreactant gases onto the walls and thereby lowers particulate generationin the chamber. The illustrated chamber thus has a longer service lifeand greater throughput, since the chamber does not have to be cleaned asfrequently.

Furthermore, by varying the thickness of the upper and lower walls inorder to control wall temperature, these walls can be provided with acontrolled temperature both across their inner surfaces and between theinner surfaces and outer surfaces of the walls. Moreover, asubstantially uniform temperature across the inner surfaces reduces theoccurrence of localized depositions which can affect the distribution ofheat within the chamber, and ultimately affect the uniformity of wafertreatment (e.g., thickness of deposition).

Deposition Uniformity and Compact Design

The present invention improves deposition uniformity for low pressureprocessing of a semiconductor wafer in a chamber having thin walls bythe design of the chamber walls. The upper and lower walls 12 and 14 aredesigned to have inner surfaces 46 and 58, respectively, which aresubstantially planar. This creates a uniform cross-sectional area overthe wafer 16. The uniform chamber height provided over the wafer leadsto a more laminar gas flow, which in turn leads to more uniformdeposition of reactant material onto the wafer. Moreover, the flat innersurfaces 46, 58 enable confined chamber volumes and faster gas flowrates, leading to faster deposition and greater throughput.

Deposition uniformity is further improved by the multiple outlet portgas system as described above and in particular, the illustrated quadragas flow system. By providing side gas outlets 26 and 28, in addition tomain gas outlet 24, gas distribution within the chamber can becontrolled to provide gas flow toward the sides of the chamber where theside outlet ports are located, as well as in a generally downstreamdirection toward the main outlet port. By tuning adjustable valves inthe outlet ports 26 and 28, laminar gas flow can be provided.

Furthermore, by improving gas flow in this manner, the chamber 10 can bemade more compact than previously designed chambers because the reactantgases do not require additional space to spread out toward the sides ofthe chamber before reaching the wafer. The gas flow configuration, byproviding multiple gas outlets in the lateral walls of the chamber,provides deposition towards the sides of the wafer without the need fora larger chamber. The chamber 10 can also be made more compact by makingthe side wall 18 out of opaque quartz in order to protect the O-rings126 found between the side wall 18 and flange 20. The opaque quartzreflects more heat back to the chamber than would transparent quartz.Therefore, the O-rings can be placed closer to the susceptor and waferwithout increasing the risk that the O-rings will heat too much or burn.

Although this invention has been described in terms of certain preferredembodiments, other embodiments that are apparent to those of ordinaryskill in the art are also within the scope of this invention.Accordingly, the scope of the invention is intended to be defined by theclaims that follow.

I claim:
 1. A single substrate thermal processing chamber, comprising: afirst wall having at least a portion thereof which allows transmissionof radiant heat into the chamber, the first wall having a substantiallyplanar inner surface and an outer surface that is at least partiallyconcavely curved over at least a portion of the wall that allowstransmission of radiant heat into the chamber; a second wall; a sidewall connected to the first and second walls to define an interiorcavity surrounded by the first wall, the second wall and the side wall,wherein the first wall forms a separation between the inside of theinterior cavity and the outside of the interior cavity to preventprocess gases from passing therethrough, the side wall having at leastone inlet port and one outlet port, wherein the substantially planarinner surface of the first wall spans substantially the entire distancebetween the inlet port and the outlet port; and a support structurepositioned within the interior cavity of the processing chamber.
 2. Theprocessing chamber of claim 1, wherein said portion of said first wallthat allows transmission of radiant heat into the chamber issubstantially transparent.
 3. The processing chamber of claim 1, whereinthe first and second walls are made of quartz.
 4. The processing chamberof claim 1, wherein the outer surface of said first wall includes acenter portion and a peripheral portion.
 5. The processing chamber ofclaim 4, wherein the center portion of the outer surface issubstantially planar and the peripheral portion of the outer surface isconcavely curved.
 6. The processing chamber of claim 1, wherein thefirst and second walls are substantially circular.
 7. The processingchamber of claim 4, wherein the center portion and the substrate areboth substantially circular and the center portion has a diameter thatis smaller than the diameter of the substrate.
 8. The processing chamberof claim 1, wherein the side wall is substantially cylindrical.
 9. Theprocessing chamber of claim 1, wherein the second wall has an outersurface that is at least partially concavely curved.